Re: [Xen-devel] [PATCH] x86: rework hypercall argument translation area setup

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.02.13 at 13:08, Keir Fraser <keir@xxxxxxx> wrote:
> On 21/02/2013 11:42, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:
> 
>> Rather than using an order-1 Xen heap allocation, use (currently 2)
>> individual domain heap pages to populate space in the per-domain
>> mapping area.
>> 
>> Also fix an off-by-one mistake in is_compat_arg_xlat_range().
>> 
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> Well, fine in principle. This manual setup/teardown of l2/l1 pagetables in
> the perdomain area is getting a bit tiresome though isn't it? Isn't there
> some setup helper that could be abstracted out for all users, and perhaps
> even some automated teardown-and-freeing on domain destroy? I just sighed
> when I saw more skanky pagetable manipulation for what is a conceptually
> simple change.

I tried to spot pieces worth folding into helper functions, but
didn't really find anything worthwhile (the purposes of the
mappings are just too different). Perhaps we could have a
map_pages_to_guest(), taking care of all intermediate page
table levels? I can't see much else, and the main problem is that
of tracking pages used for page tables here anyway.

Are we concerned about the performance of guest GDT/LDT page
(un)mappings?

Jan


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